Telephone system



July 2, 194-0. J. DAVIDSON. JR 2,206,544

TELEPHONE SYSTEM Filed July 19, 1939 2 Sheets-Sheet 1 SELOND wn-muprm INTERRUPTER lNl/EN TOR J. DAVIDSON JR.

ATTOQNEV July 2, 1940.

J. DAVIDSON. JR 2,206,544

TELEPHONE SYSTEM Filed July 19, 1959 E Q/PO/ v lNVE/VTOR By J. DAV/DSON JR.

WWWLMW ATTORNEY 2 Sheets-Sheet 2 Patented July 2, 1940 2,206,544

UNITED STTES PTET v 2,206,544 TELEPHONE SYSTEM John Davidson, Jr., Montclair, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 19, 1939, SerialNo. 285,226

8 Claims. (01. 1796.3)

This invention relates to telephone systems and and when opened this switch s-evers the ground particularly to automatic and semiautomatic sysconnection. With this arrangement the coin tems having coin controlled lines. ground at the substation is removed during the 6 An object of the invention is to improve the transmission of impulses from the dial and is condialing operation involved in establishing connected to the line at all other times whether the nections and to simplify the equipment by obviatdial is in its normal position or is held in some ing the necessity of providing impulse repeaters. off-normal position by the patron. Any effort on Another object of the invention is to guard his part, therefore, to defeat the collection of the against the fraudulent operation of the coin discoin by holding the dial off-normal after finishing posal mechanism. his conversation would be unsuccessful. The 10 Another object of the invention is to simplify switch for controlling the coin ground may com- I the mechanism necessary to distinguish between prise a small tube containing a globule of mercalls completed automatically and calls comcury which closes the circuit contacts when the u pleted with the assistance of an operator. dial is at rest and which is moved out of engage- It is the usual practice in coin controlled telement'with these contacts by the centrifugal force phone systems to connect the coin line to ground produced when the dial is rotating. at the substation in response to the deposit of Another feature of the invention is a system the coin. Since the presence of this ground conin which the release of a connection, established m nection at the substation reduces to some extent fully by automatic switches under the control of the strength of the impulses transmitted by the the calling patron, depends upon a successful substation dial, it has also been the usual practice test for the presence ofa coin ground at the end to provide an impulse repeater in the central ofof conversation followed by the removal of said rice for repeating the dialed impulses to the ground, and in which the operation of the selector selector switches. These impulse repeaters reswitch under the control of the dial to extend quire additional apparatus, and it has been prothe calling line to an operators position results in posed to dispense with them by providing oiftheoperation of means for canceling the requirenormal contacts on the dial for disconnecting the ments for said test in order that the connection coin ground from the line during the interval that may be released at the end of conversation impulses are being transmitted to the central of- Whether or no t e e is e d p s ed co n to be fice. However, the use of an oil-normal contact disposed o at the Calling non the dial for controlling the connection of the These and other features of the invention will coin ground to the subscribers line makes it posbe d ed in de a in e ow ng pecificas-ible for the patron at the coin station to intertion and W a o be Set forth in the appended fere with the disposition of the deposited coin elaimS- I by the controlling circuits at the central office. In the drawings accomp y g the speo fioa- For example, the calling patron, having deposited tion, Figs. land 2 illustrate the circuit details a coin and completed his conversation, might of an at c telephone sys incorporating move the dial away from its normal position to e featuresof the present invention. open the coin ground and defeat the attempt of 1 d o s a telephone line q pp With the equipment to collect the coin. coin controlled mechanism and also shows a line- 40 According to the present invention advantages finder Swi ch and a coin trunk circuit in the over these prior arrangements are secured by central oifice; means of a system in which the use of an im- Fig. 2 illustrates, largely in diagrammatic manpulse repeater is obviated without exposing the her, the selector and connector switches in the system to the liability of fraudulent interference central office for extending connections to sub- 5 on the part of the coin patron. scribers lines and to operators positions; and

A feature of the invention whereby these ad- Figs. 3 and 4 are views of an impulse transvantages are secured is a coin controlled substamitter suitable for use at the substation of the tion in which the impulse transmitting dial is coin line shown in Fig. 1.

equipped with a switch which is closed at all I Referringparticularly to the drawings, the pay 0 times the dial is at rest and which is opened autostation line we is equipped with the usual transmatically by centrifugal force at all times the mitter Illl, receiver 102, ringer I03 and coin dis dial is in motion. When closed this switch composal magnet Hit. The pay station is also pletes the ground connection through the coin equipped with an impulse dial I 05 having the controlled contacts and the coin disposal magnet, usual contacts I96 for transmitting impulses and yea off-normal contacts I01 for opening the receiver circuit and for closing a short circuit around the transmitter I M. In addition to these contacts, the impulse transmitter is provided with a pair of contacts I08 and I09 which are opened and closed by a globule of mercury I I0 contained 'within the tube III.

The mercury switch associated with the impulse transmitter I is shown in greater detail in Fig. 3 of the drawings. This switch comprises a small tube III which is mounted by means of a suitable clamp II 2 on a rotating part of the dial, such as the plate H3. Plate H3 is secured to the rotatable shaft H4 and rotates therewith in response to any manipulation of the fingerwheel H5. The tube III is mounted at an angle to the plate H3, as indicated in the drawings, so that the globule of mercury IIZI remains in the end of the tube when the plate H3 is at rest. In this position of rest, the mercury globule IIU closes the circuit including the contacts I08 and I65. By selecting the angle at which the tube I I I is mounted with respect to the plane of rotation of the dial, it is possible to maintain a closure between contacts I08 and I09 at all times and in all positions of the dial, except when it is rotating at least as fast as its impulse sending speed. However, When the dial is rotating for the purpose of sending impulses to the central omce, it produces enough centrifugal force to move the mercury globule out of contact with terminals IE8 and I09.

The pay station line I00 appears at the central office in aline circuit, including the line relay I I! and the cut-ofi relay H8, and in the banks of line-finder switches such as the finder F.

The line finder F and the first selector switch S are interconnected by a coin trunk circuit T. The trunk T includes the necessary relays and other devices for controlling the disposition of the deposited coins and for controlling the estab- Zishment and release of the coins. It will be noted that the coin trunk T does not include the repeater generally required for repeating impulses from the dial at the pay station to the succeeding switches. Instead, the impulses sent by the calling patron are transmitted directly to the stepping magnets of the switches, and this is made possible by the mercury switch II I, which responds to the movement of the dial and disconnects the coin ground from the line so that it does not interfere with the transmission of the dial impulses.

The first selector S has access through certain of its contact levels to subscribers lines by way of succeeding switches, such as the selector switch S I and the connector switch C. The first selector S also has access through a particular one of its levels, such, as the tenth level, to operators positions by Way of operators trunks, such as the trunk TI.

While the invention is not limited to systems using any particular form of selector switch for establishing the connections, it has been illustrated herein in a system employing the wellknown step-by-step type of switch. Also, the coin mechanism at the pay station may be of any suitable and Well-known type.

The system will now be described in detail, assuming first that a patron at the pay station of the coin line I99 wishes to call the subscriber of a local line 200. To initiate the call a coin I20 is deposited in the box and the receiver I02 is removed from the switchhook. I2I. A circuit is then closed from battery through the winding of the slow-release line relay II'I, back contacts of cut-cit relay H3, over the line conductor I22, closed switchhook contacts, contacts I06 of the dial I05, transmitter IIII, coil I23, through the coin magnet I04, coin contacts I24, thence to 5 ground through the closed contacts of the mercury switch III. Relay III through its left contacts places a calling potential on the sleeve terminal of the finder F. At its right contacts the line relay Ill closes the start circuit I 25, and the line finder hunts for the calling line.

The line finder F seizes the calling line in the well-known manner and extends it through to the first selector S. A circuit is now closed from battery through the right winding of the impulse relay ZII I, thence through the winding of polarized relay I28, normal contacts of relay I27 through the lower normal contacts of relays I28 I29, through the middle brush of finder F, conductor I22, thence through the substation loop and returning over conductor I30 through the upper brush of finder F, upper back contacts of relays I20 and I28, through the left winding of relay ZEH to ground. The direction of current flow in this circuit is such that the polarized relay I26 does not operate. Relay 20I operates and, in the well-known manner, causes the application of holding ground potential to the sleeve conductor ISI. Ground on conductor I3I causes the operation of relay I32 in an obvious circuit. The cut-off relay H8 is also operated in a circuit from battery, through the winding thereof, left contacts of relay I H, thence over the sleeve brush of the line finder F, conductor I33, normal contacts of relay I34 to ground on conductor I3I. Relay H13 looks through its own front contact to the grounded sleeve conductor and releases the line relay II I. I

When relay I32 operates, it closes a circuit from ground through its right contacts, conductor I35, and thence in a parallel circuit through the winding of slow-release relay I35 to battery and lower back contacts of relay I41, Winding of relay I34 to battery. Relay I36 operates and closes an obvious locking circuit for relay I34. Relay I-M at its make-before-break contacts disconnects sleeve conductor I3I from sleeve conductor I33 and closes a substitute circuit for maintaining ground potential on conductor I33. Relay I35 in operating closes a locking circuit for itself from battery, through the Winding thereof, lower back contacts of relay I 31 to ground at the contacts of relay I36. A second locking circuit of relay I36 is also closed from battery through the winding thereon, conductor I35, lower back contact of relay I41 to ground at the contact of relay I35.

The calling patron now manipulates the dial I05 to send impulses, causing the operation of relay 2M and the setting of the selector switch S. Thereupon the relay 2M is disconnected from the line, and the next series of impulses sets the succeeding selector switch SI to seize a trunk extending to an idle connector switch C. As soon as the connector C is seized a circuit is closed from battery through the lower winding of relay 202, lower normal contacts of relay 203, thence over the lower side of a connection through the trunk T and finder F and over the loop of the calling line as previously traced and returning over the other side of the connection through the upper normally closed contacts of relay 203, upper winding of relay 202 to ground. As before, the polarized supervisory relay I 26 does not operate when current flows in this direction. Impulse relay 202 in the connector C operates the slow-release relay 204 which applies holding ground potential to the sleeve conductors 205 and I3I. Finally, the calling patron transmits the last two series of impulses in the designation, and the connector switch C is operated to seize the called subscribers line 200.

When the called subscriber answers, the usual circuit is closed for the operation of the supervisory relay 203, and this relay operates to reverse the direction of current flowing through the windings of relay 202 back over the extended connection, including the calling line. This re versal in the direction of current flow causes the operation of polarized supervisory relay I23, and a circuit is closed from battery through the winding of relay I28, contacts of relay I26 tothe grounded conductor I35. Relay I28 closes an obvious operating circuit for relay I38, and the latter relay looks through its own contacts to the grounded conductor I33. The operated condition of. relay I33 is an indication that the call has been established successfully and that the coin should be collected at the termination of conversation. Relay I28 also introduces a reversal in the tip and ring conductors of the coin trunk T. The purpose of this reversal is to restore control of the supervisory relay 202 in the connector switch to the switchhook contacts at the calling station so that the connector will be released when the calling patron replaces his receiver on the hook. Following the reversal by the relay 203, the lower winding of relay 202 is connected to the tip conductor I30 of the calling line, and this conductor is connected to ground through the coin contacts independently of the switchhook I2I. Therefore, unless and until the coin is disposed of, the relay 232 in the connector switch may be held to prevent the release of. the connection, This is avoided, however. as above explained, by introducing the second reversal in the tip and ring conductors by operating the relay I28.

When the subscribers have finished conversing, they replace their receivers on the switchhooks, and relays 202 and 203 release. After an interval, relay 204 releases and ground is removed from conductors 205 and I3I, permitting the restoration of selectors S and S-I and connector C. The removal of ground potential from conductor I3I causes the release of relay I32, but relay I36 remains operated as above explained. Relay I34 also remains operated and maintains ground potential, on the sleeve conductor I33 to hold the line-finder switch F.

As soon after relay I32 releases as the rotating interrupter I39 advances'to-one of its conducting segments, a circuit is closed over the back contacts of relay I32, front contacts of. relay I34, contacts and winding 'of relay I40 to battery. Relay I40 operates and locks throughits own contactsto the grounded conductor'uI33, Relay I40 closes an obvious operating circuit for relay I29, and the latter. relay disconnects the 'tipiand ring conductors of the coin line from the corresponding conductors of the trunk T and connects them in simplex relation to the upper armature of relay I31. Following the operation of relay I40, the relay I31 is operated and released repeatedly under the control of the rotating interrupter I4I, the circuit forrelay I31 extending through the contacts of relay I40 to the interrupter I4I. Each time the relay I31 operates it closes a circuit from the positive poleof the coin collect battery I42 through the front contacts of relay I38, winding'of relay I43, contactsof relay I31, through the front contacts of relay I29, over the conductors. of the coin line, through the windings of the coin disposal magnet I04, closed contacts I24, conductor I44, through the con-- tacts I08 and I09 of the mercury switch to ground. The polarized magnet I04 energizes in this circuit and operates its armature in the proper direction for collecting the deposited coin I20. If the magnet is'not successful in collecting the coin in response to the first energization, the relay I31 continues to operate under the control of interrupter MI to apply successive impulses of coin collect current to the line. It will be noted that the relay I31 at its lower contact opens one of the locking circuits of relay I30 each time the coin battery I42 is applied to the coin line. During the first of these intervals, however, the relay I33 is maintained energized over its other locking circuit, which extends through the lower back contact of relay I41. Also, during the first application of. coin current to the calling line, relay I43 operates and closes a substitute holding circuit for relay I36. At the same time relay I43 operates relay I41 in an obvious circuit, and the latter relay locks through its upper front contact to the grounded conductor I33. On each succeeding application of coin potential to the line, relay I36 depends solely for its maintained operation on the circuit closed at the front contacts of relay I43. As soon as the coin is collected and the coin contacts I24 are opened the circuit for relay I43 is severed. Upon the next operation of relay I31 under control of interrupter I4I- the holding circuit of relay I 36 is opened and held open for an interval sufficient to permit the release of the latter relay. Relay I30 opens the holding circuit of relay I34 and the latter relay releases and removes ground potential from the sleeve conductor I33. The removal of ground from sleeve conductor I33 causes the restoration of the line finder F and the release of all associated relays.

It will be noted that the finder switch. F is not permitted to release at the end of a call until the coin trunk determines, first, the presence of the coin ground at. the calling pay station, and then the removal of said ground from the line. Since this coin ground is connected through the contacts I08 and I 09 of the mercury switch II I to the line when the dial is in any resting position and is disconnected from the line only while the dial is rotating, any attempt on the part ofthe patron to prevent'the disposition of the coin by holding his dial on normal will be unsuccessful. By properly designing the mercury switch III, the mercury globule -IIO can be made to close the contacts I03 and I 09 at all times except when the dialis rotating at a speed commensurate with the speed at'whichit restores to normal during the sending'of impulses; At slower speeds and at'the stopping points of the dial, the mercury globule immediately recloses the contacts and consequently the coin collect circuit.

If the call to the subscribers line 200 is unsuccessful, that is, if the line is found busy or the called subscriber fails to answer, the supervisory relay 203 does'not operate as above de- When, thereafter, the calling patron replaces his receiver on the switchhook relays 202 and 204 release, and the selector and connector switches restore as above described. The relay I 31 is operated under the control of interrupter I as previously explained, but the negative pole of the coin refund battery I46 is now connected to the tip and ring conductors of the calling line. Consequently, the magnet I04 at the substation operates its armature in the proper direction for refunding the coin to the calling patron.

Assume next that the patron of the coin pay station wishes to make a call for which the services of the operator at position 0 are required. He initiates the call in the same manner, by depositing a coin in the box and removing his receiver from the switchhook. After the finder has found the line and extended it through to the first selector switch S, the calling patron manipulates his dial I05 to transmit a series of ten impulses. These impulses operate the selec tor switch S to the tenth level of terminals, and the switch hunts in this level and seizes an idle trunk T--I extending to the operators position.

As the seiector S reaches its tenth level position the cam 20'! closes the level contacts 208, and these contacts remain closed until the switch is released from this level. Contacts 208 close a circuit over conductor 209, through the winding of relay I21 to battery. Relay I21 at its contact closes an operating circuit for relay I41, and the latter relay operatesand locks to the grounded conductor I33. At its inner upper contact relay I21 closes an obvious operating circuit for the charge relay I38, and the latter relay looks through its lower contact to the grounded conductor I 33.

When the selector S extends the connection through to the operators trunk T-I, a circuit is completed from battery through the upper winding of relay 2I0, back contacts of relay 2I I, thence over the lower side of the connection,

trough the lower front contacts of relay I21, lower back contacts of relay I28, thence as above traced over the calling line and returning over the upper side of the connection through the inner upper back contacts of relay I28, through the upper brush of selector S, upper back contacts of relay 2 to ground through the lower winding of relay 2H]. Relay 2I0 operates relay M2 and slow-release relay 2I3 in obvious circuits. Relays 2h! and 2I3 apply ground potential over conductor 2I4 through the right winding of coil 2I5, sleeve conductor 2H5, thence to sleeve conductor I 3| to hold relay I32 operated. Relay 2I2 also lights the lamp 2II as a calling signal to the operator.

When the operator responds by inserting the plug of her cord circuit C-I in the jack of the trunk TI, the sleeve relay 2 is operated in the well-known manner, disconnecting the relay 2H] from the tip and ring conductors of the trunk. Relay 2H at its inner lower contact closes a substitute holding circuit for relay 2I3 to maintain ground potential on the sleeve conductor 2H5. Relays 2H] and 2I2 release and the lamp 2!! is extinguished. The operator at position 0 converses with the calling patron and establishes the connection he desires. By means of the usual coin disposal circuits (not shown) the operator is able to refund the coin deposited at the pay station in the event no charge is necessary or to make any collections that may be required. Or, if the circumstances require it, the operator may request a deposit of the necessary coins for the connection she has established and permit the coin trunk T to collect these coins automatically at the end of conversation.

Assume that the operator succeeds in establishing the connection desired by the calling patron and that coins have been deposited in the box at her request in payment for the call. After the conversation is finished the calling patrons replaces his receiver I02 on the switchhook I2I. and the operator is given the usual supervisory disconnect signal. When she withdraws the plug of her cord circuit from the jack of trunk TI, relay 2 releases and releases slow-release relay 2 I 3. Relay 2 I3 removes ground potential from the sleeve conductors 2I6 and I3I and relay I32 restores to normal. Relay I41] operates on the next closure of interrupter I39, causing the operation of relay I29 as above explained. On the next closure of interrupter I4I, relay I3! operates and connects the tip and ring conductors of the calling line through the winding of relay I43 and the front contact of relay I38 to the coin collect battery I42. The coin magnet I04 operates to collect the coins, and, on the next operation of relay I31, relay I36 releases since relay I43 does not operate in this case and since relay I41 is already operated and looked as above explained. Relay I34 new releases, and the finder F and coin trunk T are restored to normal condition.

Assume that the operator collected the coins deposited at the pay station before the connection is released at the end of conversation. Under these conditions it is necessary for the coin trunk T to eflect a release of the finder switch F without first testing for the coin ground and then for the absence thereof. It is possible for the trunk T to accomplish this result by reason of the fact that relay I41 was operated and locked at the time the selector switch S advanced to its tenth level position. On the first operation of relay I3'I under the control of interrupter I4I at the end of the call the coin disposal circuit is closed through to the coin collect battery I42 as previously described. Since, however, the coins were previously collected by the operator, no ground potential exists at the substation, and relay I43 remains inert. Hence, relay I36 releases on the first operation of relay I31 since relay I4! is already operated and locked and relay I43 fails to operate. Relay I36 thereupon releases relay I34, and the finder switch is permitted to restore to normal, releasing the coin line for further use.

In this manner the coin trunk T is able to discriminate between a call to a subscribers line and a call to the operators position for the purpose of effecting the release of the coin line and line-finder switch, on a call to the operator, without requiring the presence of the coin ground at the pay station.

What is claimed is:

1. In a telephone system, a telephone line having a pay station thereon, automatic switches for extending said lines, an impulse dial at said pay station for operating said automatic switches, means responsive to the deposit of a coin at said station for establishing a ground connection to said line, and a set of normally closed contacts controlled by the movement of said dial and opened only while the dial is in motion for removing said ground connection from the line.

2. In a telephone system, a telephone line having a pay station thereon, automatic switches for extending said line, an impulse dial at said pay station for operating said automatic switches, means responsive to the deposit of a coin at said station for establishing a ground connection to said line, and a switch operated by the rotating movement of said dial for opening said ground connection and for maintaining said connection closed at all times the dial is at rest.

3. In a telephone system, a telephone line having a pay station thereon, automatic switches for extending said line, an impulse dial at said pay station for operating said automatic switches, means responsive to the deposit of a coin at said station for establishing a ground connection to said line, and a switchoperated by the centrifugal force produced by the rotation of said dial for opening said ground connection and for maintaining said connection closed whenever the dial is at rest.

4. In a telephone system, a telephone line having a pay station thereon, automatic switches for extending said line, an impulse dial at said pay station for operating said automatic switches, means responsive to the deposit of a coin at said station for establishing a ground connection to said line, a switch including a sealed tube attached to said dial, a globule of mercury in said tube movable by the centrifugal force produced by the rotation of said dial, and'switching contacts closed by said globule to maintain said ground connection closed whenever the dial is at rest and opened by the movement of said globule while the dial is rotating.

5. In a telephone system, a telephone line having a pay station thereon, automatic switches for extending said line, an impulse dial at said station for operating said automatic switches, a coin receptacle and a coin disposal magnet at said pay station, a normally open connection from said line through said magnet to. ground, contacts controlled by the deposit of a coin in said receptacle for closing said ground connection, means for applying current over a circuit including said line and said ground connection for operating said magnetto dispose of a deposited coin, and a switch having contacts con trolled by said dial for closing said ground connection in any rotary position of the dial provided the dial is at rest and for opening said ground connection in response to the rotary movement of said dial.

6. In a telephone system, a calling line having a pay station thereon, an impulse dial at said pay station, means responsive to the deposit of a coin at said pay station for establishing a ground connection to said calling line, a central ofiice in which said line appears, a called line, an operators position, an automatic selector switch, other automatic switches, means in said central ofilce for extending a connection from said calling line to said selector switch, means responsive to said dial for operating said selector switch to extend the calling line to said operators position or to extend the calling line by way of said other automatic switches to said called line, means for disposing of a coin deposited at said pay station after a call has been extended to said called line, means dependent on the presence of said ground connection and on the subsequent removal there of for effecting the automatic release of said calling line, and means controlled by said selector switch when a connection is extended to said operators position for rendering the automatic release of said calling line independent of the presence of said ground connection.

7. In a telephone system, a calling line having a pay station thereon, an impulse dial at said pay station, means responsive to the deposit of a coin at said pay station for establishing a ground connection to said calling line, a central office in which said line appears, a called line, an operators position, an automatic selector switch, other automatic switches, means in said central ofiice for extending a connection from said calling line to said selector switch, means responsive to said dial for operating said selector switch to extend the calling line to said operators position or to extend the calling line by way of said other automatic switches to said called line, means responsive to the replacement of the receiver at the calling pay station for disposing of a coin deposited thereat, means responsive to the replacement of said receiver and dependent on the presence of said ground connection and on the subsequent removal thereof for effecting the automatic release of said calling line, and means dependent upon the position taken by said selector switch when a connection is extended to said operators position for rendering the release of the calling line independent of the presence of said ground connection.

8. In a telephone system, a calling line having a pay station thereon, means responsive to the deposit of a coin at said pay station for establishing a ground connection to the conductors of said line, an impulse dial at said pay station, called subscribers lines, an operators position, a selector switch having terminals appearing in a plurality of groups, succeeding selector switches, a line finder for extending a connection from said calling line to said selector switch, means responsive to the operation of said dial for operating said selector switch to certain of said groups JOHN DAVIDSON, JR. 

